Generally, transmitters and receivers in radio equipment utilize the same antenna. Accordingly, the transmission network controls both the transmission signal and the receiving signal. By so doing, the signal from the antenna is directed to the receiver without any substantial interference from the transmitter, and the signal from the transmitter is transmitted to the antenna without interference from the receiver.
Ceramic filters are typically employed in radio equipment to reduce substantial interference. In particular, duplex ceramic filters including two individual band-pass filters are employed. One filter connects the receiving branch and has a center frequency and bandwidth corresponding to the receiving band. The other filter connects the transmission branch and has a center frequency and bandwidth corresponding to the transmission band.
Conventional ceramic filters include a dielectric ceramic material for the main body upon which metallic materials are applied for producing conducting paths. These paths define the performance of the filter and for realization of pads or other isolated conducting areas that contact the printed circuit board or other interface material. An essential aspect of the performance of a given filter or duplexer device is the Q factor.
The Q factor or simply Q defines the loss in the filter. The relationship between the total Q of a given device and the Q factors of the ceramic dielectric material and the conducting paths and/or areas is defined by: 1/Qtotal=1/Qdielectric+1/Cconducting. Typically the Q of the dielectric material is much higher than the Q of the conducting paths and/or areas. As a result, the overall Q of the filter is predominantly determined by the Q of the conducting paths and/or areas.
Dielectric filters compete with air dielectric filters which exhibit Q factors on the order of 20,000 and higher. Meanwhile, high quality ceramic filters exhibit Q factors on the order of 2,000. What is needed in the art is a method of designing a dielectric filter with Q factor values approaching those of air dielectric filters. What is also needed in the art is a dielectric filter having a specific arrangement of conductive materials resulting in a high Q factor resembling that of an air dielectric filter.